And also it seems like the "function" of a given neurotransmitter is made all the less clear in light of how some of its receptions activate excitatory signals and some activate inhibitory signals. Thus the function of a given neurotransmitter is partially exogenous to its chemical structure, if I understand correctly.
This is all to say, the dopamine argument as it is often employed seems facile and almost pseudoscientific to me, if even incidentally accurate in many cases.